Self-contained cryogenic refrigerator



Aug. 8, 1967 K. w. COWANS SELF'CONTAINE-D CRYOGENIC REFRIGERATOR 5Sheets-Sheet 2 Original Filed Jan. 18, 1965 aka 2 Armzwsd SELF-CONTAINEDCRYOGENIC REFRIGERATOR Original Filed Jan. 18, 1965 I) Sheets-Sheet I55c r/aA 0; Am? caw zssae I United States Patent O- 3,334,491SELF-CONTAINED CRYOGENIC REFRIGERATOR Kenneth W. (Iowans, Los Angeles,Playa Del Rey, Calif., assignor to Hughes Aircraft Company, Culver City,Calif., a corporation of California Continuation of application Ser. No.426,174, Jan. 18, 1965. This application Sept. 14, 1966, Ser. No.589,154 16 Claims. (Cl. 62-45) ABSTRACT OF THE DISCLOSURE The devicecomprises a self-contained cryogenic refrigerator associated with acondenser which comprises a normally closed refrigerating loop to a heatload. Refrigeration is provided at the condenser and the cryogen in therefrigerating loop is cooled to liquefaction and is transferred via aLeidenfrost transfer technique to a heat load and there evaporated toprovide heat load cooling. The cryogen in the refrigerating loop may bedrawn from ambient air and exhausted back to atmosphere when the systemis turned off. The sealed refrigerator disclosed includes compressionand expansion pistons operating in 90 out-of-phase relationship to eachother.

This application is a continuation of Kenneth W. Cowans, Ser. No.426,174, filed Jan. 18, 1965, entitled Self-Contained CryogenicRefrigerator.

This invention relates generally to cryogenic refrigeration and relatesmore particularly to an improved closed cycle refrigerator which cools aremote heat load to cryogenic temperatures either continuously orintermitently.

The performance of many critical electronic components can be greatlyimproved by cooling them to cryogenic temperatures; For example, theperformance of infrared detectors and parametric amplifiers is greatlyimproved by cooling them to low temperatures. Cryogenic cooling of thesecomponents in certain field installations, such as airborne equipment,has resulted in the development of several refrigeration systems suchas: open cycle thermomechanical systems; and closed cyclethermomechanical systems.

In the prior art open cycle refrigeration systems, a supply of cryogenis stored in a flask, transferred to a heat load, such as an infrareddetector, allowed to vaporize in a controlled manner, and then vented tothe atmosphere. Thus, improved performance from the heat load is obtained. Once the supply of cryogen is exhausted, the system must berecharged with another supply of liquid cryogen. One example of an opencycle refrigeration system is described in U.S. Patent No. 2,996,893,issued Aug. 22, 1961, to J. G. Goodenough et al.

In the closed cycle cryogenic refrigerator, a reservoir of liquidcryogen is also provided and transferred to a heat load and allowed tovaporize in a controlled manner, thereby providing refrigeration. Withthese closed cycle systems, however, the expanded gaseous cryogen isreliquefied and fed back to the reservoir for recirculation through thecycle rather than being vented to the atmosphere. One example of aclosed cycle cryogenic refrigerator is described in US. Patent No.3,126,711, issued Mar. 31, 1964 to L. E. Miller.

An object of this invention is to provide a device for improved cryogentransfer between a gas liquefier and a heat load.

Another object of this invention is to provide an improved closed cyclecryogenic refrigerator that can be operated continuously orintermittently and which is not operationally affected by beingcompletely turned off for long standby periods between operations.

' 3,334,491 Patented Aug. 8, 1967 Still another object of this inventionis to provide an improved cryogenic refrigerator employing a closed looprefrigeration cycle and designed to avoid leakage or escape of cryogen.

Still another object of this invention is to provide a lightweightsealed cryogenic refrigerator which is easily maintained andtransported.

Yet another object is to provide an improved cryogen transferarrangement that utilizes atmospheric air as a reservoir of cryogen andwhich is not affected by contaminants in the atmospheric air.

The above and other objectives of this invention are accomplished byproviding a self-contained cryogenic refrigerator transfer arrangementhaving two closed loops: an inner closed loop which receives the inputpower and provides refrigeration; and an outer closed loop whichutilizes atmospheric air as the cryogen and transfers the refrigerationeffect from the inner loop to a heat load.

The inner loop includes an improved gas refrigerator which operates onthe Stirling cycle or the Ericsson cycle. The refrigerator includes acompression chamber and an expansion chamber which are operativelyformed by a compact folded piston arrangement in which the two pistonsoperate out of phase with one another and reciprocate along intersectingaxes from a common cranlo shaft. The compression chamber isinterconnected with a regenerator of the expansion chamber through aheat exchanger having heat transfer fins so that the heat of compressioncan be transferred from the refrigerator to a heat transfer medium. Theentire gas liquefier is hermetically sealed with only the cold portionbeing thermally insulated so that the refrigerant is transferred backand forth between the compression chamber and the expansion chamberuntil the temperature of the refrigerant in the expansion chamber dropsto a low level. Preferably, the refrigerant is dropped to a temperaturelower than the boiling pointof liquid air (77 K. nominal).

The outer loop is connected between the cold expansion chamber of therefrigerator and in thermal transfer association with the heat load. Inoperation, refrigeration from the refrigerator (inner loop) istransferred to a cryogen in the outer loop through a condenser whichliquefies the cryogen of the outer loop. Continuous circulation of thiscryogen in the outer loop is accomplished by means of a low pressurecompressor which provides a pressure gradient for moving the liquefiedcryogen to the heat load and drawing expanded cryogen away from the heatload.

The outer loop utilizes ambient atmosphere for the cryogen. Thus, tocompensate for any variation in internal pressure in the outer loopresulting from the substantial volumetric change between liquid cryogenand gaseous cryogen, the outer loop is selectively communicated with theambient atmosphere (air) through a self-purging filter means, wherebyany contaminants in the incoming air are entrapped in the filter. Whenthe internal pressure of the outer loop exceeds a predetermined level,the cryogen (air) is vented back out through the filter. In addition,any impurities previously entrapped in a filter are transferred back tothe atmosphere by an automatic purging system when the system is on andthe filter is not being used. An advantage of this arrangement is thatthe atmospheriFair is used for a reservoir to supply cryogen, therebyeliminating the need for a cryogen storage vessel.

Transfer of the cryogen between the outer loop and p the heat load isaccomplished through flexible transfer it layer is formed. Eflicientformation of these droplets is accomplished by means of a heat exchangetechnique in which the heat of the returning expanded cryogen gas, whichis above the boiling point of the liquid cryogen, is transferred to theoutgoing droplets, thereby causing the boundary layer to form around thedroplets. In addition, cold from the cryogen droplets is transferred tothe expanded incoming cryogen, thereby resulting in a more eflicientheat transfer operation.

A heat load that may be used with this device includes a Dewar flaskhaving the electronic component positioned at one end thereof. Thus, theincoming cryogen droplet-s enter the Dewar and cool the electroniccomponents, resulting in a certain amount of the cryogen boiling off.The boiled-off cryogen is transferred back by the compressor in theouter loop, recirculated, and reliquefied by heat transfer from theinner loop gas liquefier. Thus, with the flexible line, a remote heatload which can be gimbaled or moved about its orthogonal axis, can becooled without moving the self-contained cryogenic refrigerator.

Other objects, features, and advantages of this invention will becomeapparent upon reading the following detailed description of oneembodiment of the invention and referring to the accompanying drawingsin which:

FIGURE 1 is a functional block diagram of the selfcontained cryogenicrefrigerator system;

FIG. 2 is a perspective view of the assembly details of the refrigeratorcontaining the inner refrigeration loop;

FIG. 3 is a vertical cross-sectional view of the refrigerator showingthe physical relationship of the folded pistons to one another and therelationship between the compression chamber and the expansion chambercontaining the two pistons; and

FIG. 4 is a schematic block diagram of the outer loop which is arrangedto circulate a cryogen (air) between the refrigerator and a heat load.

Referring now to the drawings, the closed cycle cryogenic refrigeratorsystem is shown in FIG, 1 as a block diagram in order to illustrate theoperational relationship between a closed inner loop and a closed outerloop. The closed inner loop includes a refrigerator 12 which is adaptedto receive input power, such as electrical energy, from a power source13 through a switch 14, and to convert the input power to refrigerationenergy.

As will be explained in more detail shortly, the outer loop includes agas liquefier or condenser which is mounted in thermal contact with thecold portion of the refrigerator 12, the latter being hermeticallysealed and thermally insulated from the ambient atmosphere. The outerloop also includes a circulator and mixer 16 which continuouslycirculates a cryogen, such as air, which is obtained from the ambientatmosphere. The cryogen contained in the outer loop is transferred intothermal contact with the cold portion of the gas liquefier 12, where itis liquefied and then transferred in droplet form to a heat load 17 viaa transfer line 18. The transfer line 18 may be a thin, flexible linebecause of a Leidenfrost transfer technique, as will be explainedshortly. At the heat load 17, the cryogen droplets collect, absorb heat,and are boiled off in gas form. Thereafter, the gaseous cryogen iswithdrawn from the heat load by the circulator via a return transferline 19. The circulator and mixer 16 includes a conventional lowpressure compressor to create a sufficient pressure gradient within theouter loop to provide continuous circulation. The mixer portion of theouter loop includes -a filter means 21 which is adapted to provide meansfor ambient air intake when the internal pressure of the outer loopfalls below a predetermined level, and to provide an exhaust path forthe gaseous cryogen when the internal pressure in the outer loop exceedsa predetermined level.

Referring now to FIGS. 2 and 3 which illustrate the refrigerator 12 indetail. The closed loop refrigerator 12 operates on an Ericsson cycle toproduce refrigeration at about 70 K. from a refrigerant such as heliumgas at 150 p.s.i.a. Structurally, the refrigerator includes a housing 22which encloses an electric motor at one end thereof for developingrotational motion along a central axis. The drive shaft of the electricmotor projects along the central axis of the housing 22 and drives asingle-stage planetary gearset which reduces the motor output shaftrotation speed. Planetary gears 23 are rotata-bly connected to a flange24 and inserted into the housing 22 so that they mesh with a sun gear(not shown) on the motor drive shaft. Annular gear 26 is conventionallyfixedly mounted for engagement with gears 23. An output drive shaft 28is thus driven by the rotation of planetary gears 23. The shaft 28carries eccentric cam 29, the latter, when assembled, being in alignedrelation with bones 31 and 32. Roller bearing 33 supports the outboardend of shaft 2?. Appropriate closure means are provided. When assembled,the bulkhead 27 is inserted within the outer housing 22 so that theupper cylinder bore 32 is in substantial registry with the axis of avertically projecting expansion chamber cylinder or housing 38. Asillustrated in FIG. 3, the horizontal large diameter cylinder bore 31has a cylindrical sleeve 39 fitted to line the surface thereof. Thevertical, small diameter cylinder bore 32 is also fitted with a sleeve41 and intersects with the cylinder bore 31 at an aperture 42a formedthrough the upper side wall portion of the horizontally extending sleeve39.

Compression and expansion chambers are formed within these cylinderbores by means of a compact folded piston array in which two pistonsoperate along intersecting axes and 90 out of phase with one another. Inoperation, as the drive shaft 28 rotates the eccentric 29, a compressionchamber piston 42 of a large diameter is reciprocally driven from leftto right by means of a connecting rod 43 riding on the eccentric 29 andpivotally connected to a pin 44 extending through the base 45 of thepiston 42. The drive shaft 28 extends through apertures 45a in the sidewall of the piston 42. The piston head 46 defines a variable volumecompression chamber 47 which is formed between a cylinder head insert 48and the sleeve 39. In addition, the piston side wall can be covered witha layer 51 of low-friction material, such as Teflon, to provide forsubstantially friction-free piston movement.

A variable volume expansion chamber 64 is formed in cylinder 38. Theauxiliary connecting rod 57 is pivotally connected at its lower end to aboss 58 formed on the connecting rod 43 and at its upper end to a pivotpin 59 extending radially through the base portion of the expansionchamber piston 56. The connecting rod 57 extends through an aperture 60formed through the side wall of the large diameter piston. The expansionchamber piston 56 is slidably mounted for vertical reciprocal motionwithin the expansion chamber cylinder 38. The lower end of the expansionchamber cylinder 38 includes a flange 61 through which suitablemechanical fasteners, such as bolts 62, can be mounted to secure theexpansion chamber cylinder to a boss 63 formed on the side wall of therefrigerator housing 22. Thus, as the expansion chamber piston 56reciprocates, the volume of an expansion chamber 64, formed at the upperend thereof, decreases and increases in accordance with the followingoperational description of one refrigeration cycle.

The refrigerator illustrated in the drawings is characterized by afour-phase refrigeration cycle including: a compression phase; a firstconstant pressure phase in which refrigerant is transferred from thecompression cylinder chamber 47 to the expansion chamber 64; anexpansion phase; and a second constant pressure phase in which therefrigerant is transferred from the expansion chamber to the compressionchamber.

As illustrated in FIG. 3, the volume of the compression chamber 47formed by the large diameter piston 42 is at a maximum volume while thevolume of the expansion chamber 64 formed by the small diameter piston56 is at one-half volume. Considering this piston relationship to be thestart of a refregeration cycle then, as the crankshaft 29 is rotatedclock-wise, the volume of both of the chambers is decreased so thatrefrigerant contained within the refrigerator undergoes compression anda pressure rise until the small diameter expansion chamber piston 56just passes beyond top dead center; that is, a compression phase isdeveloped by the refrigerator until the expansion chamber volume startsto increase from substantially zero volume.

Starting from this top-dead-center position, a first constant pressurephase is developed as the small diameter piston 56 moves downwardincreasing the volume of the expansion chamber 64 and, as the largediameter piston 42 continues to move to the right, decreasing the volumeof the compression chamber 47. During this phase, there is a refrigerantflow from the large diameter compression chamber 47 to the smalldiameter expansion chamber 64 with little or no pressure changeoccurring in the refrigerant or gas over the following gas path.

The refrigerant in traveling from the compression chamber 47 to theexpansion chamber 64 passes: through gas ports 66 formed in the cylinderhead 48; through heat exchanger channels 67; to an inlet port 68 in thelower end of the small diameter piston 56; upward through a thermalregenerator 69 located within the piston 56; and out slots 71 into theexpansion chamber 64.

As the refrigerant travels through the heat exchanger channels 67 itgives up the heat of compression created during the precedingcompression step to ambient atmosphere surrounding the refrigeratorhousing 22. Structurally, the heat exchanger includes a plurality ofcircumferentially extending channels 67 formed in parallel rows alongthe inner wall of the refrigerator housing 22. The circumferentiallyextending walls between the individual grooves (FIG. 1) increase theheat transfer area and heat transfer efficiency from the refrigerantthrough the heat-conducting refrigerator housing 22 to ambient.

After the refrigerant leaves the heat exchange channel 67 at aboutambient temperature and enters the thermal regenerator 69 it then flowsupward to the small diameter expansion chamber 64. During this constantpressure gas transfer the temperature of the refrigerant within thesmall diameter expansion chamber 64 is colder than the temperature ofthe gas within the heat exchanger 67. Thus, the refrigerant transfersheat to the regenerator 69 as it flows upward toward the expansionchamber. As a result, the temperature difference between the ends of theregenerator 69 varies evenly with the colder end being adjacent theexpansion chamber 64.

Structurally, the gas flow path to the regenerator includes an oblonggas port 68 formed through the side wall of the small diameter piston 56at a position between the two lower piston seals 70. Thus, as the smalldiameter piston 56 reciprocates, it is in constant gas communicationwith the heat exchanger channel 67. The refrigerant entering the gasport 68 travels upward into a. lower integrator 76 having a somewhatconical cross section and a plurality of radially projecting slotsformed in its outermost portion. Thus, the incoming refrigerant isevenly distributed to the packing of the regenerator 69. The

packing of the regenerator can be in the form of stacked screens, steelwool, or the like. The upper end of the small diameter piston enclosesan upper integrator 77 which is somewhat disk shaped but still has thesame radially projecting slots formed through the outermost portionthereof. The refrigerant escapes from the regenerator packing and theupper integrator through the slots 71 formed in the piston side wallnear the piston head and flows into the expansion chamber 64 atsubstantially the same temperature as the refrigerant already containedin the expansion chamber 64. Because the refrigerant cools in passingfrom the compression chamber 47 to the expansion chamber 64, the gaspressure does not substantially change since the density of therefrigerant increases sufficiently upon cooling to compensate for anydecrease in the refrigerant volume when filling the small diameterchamber from the large diameter chamber.

An expansion phase is initiated as the large diameter piston 42 passestop dead center and the volume of the large diameter compression chamberbegins to increase while the volume of the small diameter expansionchamber 64 continues to increase. This increase in the total systemvolume causes a pressure drop within the system resulting in a transferof work out of the refrigerant contained in the small diameter expansionchamber 64. This transfer of work out of the refrigerant creates arefrigeration potential within the small diameter expansion chamber 64which evidences itself by a lowering of the temperature of therefrigerant contained within the expansion chamber 64. Thus, it is thenpossible to utilize this refrigeration by placing a warmer object inthermal contact with the expansion chamber cylinder 38. Preferably, thewall of the expansion chamber cylinder should be thin and made of anefficient heat conducting material.

As the small diameter piston 56 leaves bottom dead center and startstraveling upward, a second constant pressure phase is initiated as thevolume of the expansion chamber 64 starts to decrease and as the volumeof the large diameter compression chamber 47 continues to increase. Therefrigerant contained within the expansion chamber 64 is transferredback to the compression chamber 47 by way of: the piston slots 71,regenerator 69, the oblong gas ports 68, the heat exchanger channels 67,and the cylinder head ports 65. As the cold refrigerant travels throughthe regenerator 69, heat is transferred from the packing to therefrigerant so that the temperature of the refrigerant increasesuniformly from the: top of the regenerator to the bottom of theregenerator. As a result, the temperature in the expansion chamber 64and at the expansion cylinder 38 is maintained as the cold portion ofthe refrigerator. When the refrigerant enters the heat exchanger channel67 it is near ambient temperature and any heat such as is acquired fromcompression or friction is transferred through the housing 22 toambient. Eventually, the large diameter piston 42 reach-es bottom deadcenter, thereby returning to the position illustrated in FIG. 3.Thereafter, the above described refrigeration cycle is repeated.

To compensate for any refrigerant leakage between the cylinder walls andthe piston seals, the large diameter piston is provided with a normallyclosed valve 81 positioned in a valve seat 82. A spiral spring 83 isconnected to the bore of piston 42 and maintains this valve 81 in aclosed position by exerting a small resilient axial force on the valvestem. As a result, any refrigerant entrapped within the crankcaseportion of the refrigerator will be transferred back to theexpansion-compression portion of the refrigerator when the pistontravels to the left to create a gas pressure differential across thepiston head sufficient to overcome the bias spring force. Therefrigeration developed by the closed cycle refrigerator is used toliquefy a cryogen of ambient fluid contained within an outer closed loopin the following manner. Referring to FIG. 3, a condenser 37 including athermally insulating housing 86 having a reentrant chamber 88 is mountedover the cold small diameter expansion cylinder 38. Thus, the coldexpansion cylinder is the only portion of the refrigerator which isinsulated from the ambient atmosphere. An interspace is formed betweenthe outer surface of the expansion cylinder 38 and the inner surface ofthe reentrant chamber 88 so that gaseous cryogen from the outer loop canbe passed upward along the surface of the cold (70 K.) expansioncylinder 38. The thermally insulating housing 87 is fastened to theflange 61 by means of the mechanical fasteners 62, thereby providing ahermetic seal between the interspace and the ambient atmosphere.

Gaseous cryogen enters the condenser 86 through an inlet line 10 whichis spiralled about the transfer line 18 to operate as a heat exchanger91 for transferring heat into the line 18. This heat develops a boundarylayer of gas about liquid cryogen droplets within the transfer line 18for a Leidenfrost transfer while, at the same time, cooling down theincoming gaseous cryogen in the line 10. An advantage of thisarrangement is that the Leidenfrost transfer technique is accomplishedin an extremely eflicient manner while providing for a more eflicientliquefaction of the incoming gaseous cryogen.

After the gaseous cryogen leaves the heat exchanger section 91, it flowsdownward through a passageway 92 extending along one wall of thethermally insulating housing 87, and enters the condenser interspace atthe lower end thereof. Because the refrigeration potential developed bythe cold expansion cylinder 38 is coldest at the upper end, this gaseouscryogen is liquefied and is transferred to the top end of the interspaceat 78 K. nominal for air. This method of cooling the outer loop cryogenreduces the heat flux downward along the material of the expansioncylinder; that is, most of the cold flowing down the cylinder wall istransferred to the gaseous cryogen flowing upward along the wall. Theliquid cryogen at the upper end of the interspace is transferred to anoutlet passageway 93 and to the thin, flexible transfer line 18. As

the liquid cryogen passes through the section of transfer line 18surrounded by the heat exchanger 91, a thin boundary layer of gaseouscryogen is formed about droplets of cryogen, whereupon the pressuredifferential developed by the boiled cryogen forces the droplets totravel through the transfer line 18.

In FIG. 4 the above-described condenser 86 is illus trated in schematicform wherein gaseous cryogen contained within inlet line 10 is fed tothe condenser 86 where it is liquefied and transferred in droplet formto a heat load 17 over the transfer line 18. The liquid droplets collectat the heat load 17 and accept heat from a device to be cooled, therebyboiling off a portion of the cryogen and returning it to its gaseousstate.

The gaseous cryogen is then returned to a first compressor section 98 ofa two-section air compressor 97 over the transfer line 19 for eventualrecirculation through a filter means to the condenser 86 and the heatload 17. As will be explained in more detail shortly, a secondcompressor section 99 draws in ambient atmosphere or air for mixturewith the cryogen (ambient atmosphere) already in the outer loop when theinternal pressure within the closed loop falls below a predeterminedlevel. It should be understood that this two-section compressor 86 is ofany conventional low pressure type that can provide a pressuredifferential for transferring a portion of the gaseous cryogen from theheat load 17 and recirculating it to the condenser 86 and heat load 17.

In operation, the gaseous cryogen is transferred from the secondcompressor section 98 to a selector valve 101 over the lines 102 and103. The selector valve 101 includes two chambers 104 and 106 which arehermetically sealed and thermally insulated from one another by adividing wall 107. Thus, when a valve plate 108 is in the pOsitiOnillustrated by the solid line representation, it is seated across oneexhaust port 109 and unseated from a second exhaust port 110. Thus, thegaseous cryogen enters the chamber 106 at inlet ports 105a, and flowsout through the exhaust port 110 and a line 112. If, however, the valveplate 108 is pivoted into the position illustrated by the dotted linerepresentation, it would be seated across the exhaust port 110 andunseated from the exhaust port 109. Under these selector valveconditions, gaseous cryogen would flow from the chamber 106 throughexhaust port 109 and a line 113 but would not flow through line 112.

Depending upon which of the above described positions the selector valve101 is in, an absorption filter 114 or an absorption filter 116 willreceive the recirculated gaseous cryogen via lines 112 or 113,respectively. The absorption filter will absorb and thereby removecontaminants from the gas and prevent freezing in the condenser 86. Toentrap these contaminants, the absorption filters can be packed with anymaterial such as activated charcoal. While the selector valve 101 is inthe position illustrated, the absorption filter 114 is receiving therecirculated gas from the selector valve 101 over line 112 and theabsorption filter 116 does not receive any recirculated cryogen gas.When, however, the selector valve plate 108 is pivoted to the positionrepresented by the dotted line, the absorption filter 116 receives therecirculated cryogen gas from the selector valve 101 over the line 113and the absorption filter 114 does not receive any recirculated cryogengas. The check valves 117 and 118 allow the recirculated cryogen to flowto the condenser 86 and isolate the filters from one another, preventingback flow of recirculated cryogen to the unused filter.

While the selected absorption filter is being utilized to entrapcontaminants from the recirculated cryogen, the other absorption filteris being cleaned or purged of any entrapped contaminants by being heatedwith a resistance heater a or 1151). A flow of ambient atmosphere fluidprovides a medium for carrying the melted contaminants from the system.This cleaning of the unused filter is accomplished by pumping ambientatmosphere (air) from the second compressor section 99 and selectivelypassing the air through the second chamber 104 of the selector valve101. Air drawn in by the second compressor section 99 is fed over a line119 to two check valves 121 and 122. If the selector valve 101 is in theposition illustrated, the gas pressure on line 112 is sufficient to keepthe check valve 122 closed, thereby sealing the gaseous cryogen flowingto filter 114 from the other flow. Since no cryogen is circulating inline 113, the gas pressure in line 113 is quite low allowing the checkvalve 121 to open and allowing the relatively warm ambient atmospherefluid to flow through the absorption filter 116. An electrical switch isconnected to the selector valve 101 so that heater 115a is turned oncausing any contaminants entrapped therein to melt and evaporate. Thecontaminants are then carried by ambient air flow from the filter 116over a line 123 to the inlet port 124 of the selector valve 101. Thiscontaminated purging air is then exhausted from the selector valve 101through an exhaust port 105 to the ambient atmosphere through a pressurerelief valve 126. If the valve plate 108 is in the second positionrepresented by the dotted line, the check valve 121 will be closed andthe check valve 122 will be open by the pressure differential in lines119 and 112 so that the relatively warm ambient atmosphere flows throughthe absorption filter 114 to evaporate any contaminants entrappedtherein. In this position, the heater 1151) would be energized by theclosure of switch 125 to melt and evaporate entrapped contaminants. Thecontaminants are then exhausted to the ambient atmosphere over a line127 to an intake port 128 of the selector valve 101 and through thepressure regulator 126.

When the pressure of the continuously recirculating cryogen containedwithin the closed loop falls below a predetermined pressure level,ambient atmosphere (air) is fed into the loop. Conversely, when theinternal pressure of the recirculated cryogen contained within theclosed loop rises above a predetermined level, the cryogen gas isexhausted to the atmosphere. For example, the internal pressure of thisclosed loop may drop when the system is first turned on as a result ofthe cryogen gas being liquefied at the condenser 86. In other Words, theliquefaction of the cryogen gas substantially reduces the volume,creating a pressure decrease. In addition, a decrease of internalpressure of the closed loop may occur during operation as a result ofgas leakage through the fittings.

T o compensate for these internal pressure variations within the closedloop, the ambient atmosphere is used as a reservoir for supplyingcryogen to the closed loop. The second compressor section 99 draws inambient atmosphere (air) and feeds it to the closed loop over the line131 through a check valve 132. Thus, when the pressure within the closedloop controlled by the first compressor section falls below apredetermined level, the check valve 132 opens, thereby allowing ambientair to enter the closed loop. This ambient air is then mixed andcirculated with the cryogen (ambient air) already contained in theclosed loop.

To regulate the rate at which the cryogen flows through the closed loop,a pressure relief valve or regulator 133 is connected to bypass thefirst compressor section 98 when the pressure differential thereacrossexceeds a predetermined level. The first compressor section 98 operatesto circulate the gaseous cryogen to insure that energy lost duringrefrigeration is transferred back to the closed loop, thereby insuringcontinuous recirculation of the cryogen.

When the system is turned off, it is possible for the internal pressureof the closed loop to increase as the liquid cryogen warms, boils, andexpands. To prevent the thin, flexible lines from bursting because ofthe internal pressure increase, a pressure relief valve 134 is connecteddownstream of the heat load 17 to vent the boiled oif cryogen to theatmosphere. This does not deplete the supply of cryogen since, aspreviously stated, the ambient atmosphere is used for a reservoir tosupply cryogen to the closed loop. As a result, the operation of thesystem is not seriously affected by long standby periods in which thesystem is turned off.

While salient features have been illustrated and described with respectto a particular embodiment, it should be readily apparent thatmodifications may be made within the spirit and scope of the invention,and it is therefore not desired to limit the invention to the exactdetails shown and described.

What is claimed is:

1. In a closed cycle cryogenic refrigerator,

a compression chamber,

" an expansion chamber,

said chambers having axes in angular relation to each other,

a large diameter piston located in the compression chamber andreciprocally movable therein,

a small diameter piston located in the expansion chamber andreciprocally movable therein, crankshaft means, power means to rotatethe crankshaft means, connecting rod means operatively linking thepistons to the crankshaft means,

whereby upon rotation of said crankshaft means said pistons are urged toreciprocally move within said chambers,

passage means interconnecting the compression chamher and expansionchamber to accommodate the transfer therebetween of a cryogen,

said passage means including heat transfer means to accommodate thedissipation of heat from said cryogen as it moves to the expansionchamber,

said pistons being reciprocally movable in out-of-phase relationship toeach other whereby the expansion of the cryogen in the expansion chamberproduces a substantial temperature fall therein.

2 Aclosed cycle cryogenic refrigerator according to claim 1,

i and including regenerating means in said passage means interposed inseries between said dissipating means and said expansion chamber.

3. A closed cycle cryogenic refrigerator according to claim 2,

wherein said crankshaft is located within a crankshaft housing chamber,

and spring-loaded valve means arranged to establish communicationbetween said crankshaft chamber and said compression chamber upon theexistence of a predetermined pressure differential therebetween.

4. A closed cycle cryogenic refrigerator according to claim 3,

wherein said pistons reciprocate along the axes in approximatelyout-of-phase relationship. 5. In a closed cycle arrangement toaccommodate transfer of a cryogen fluid liquefied to a cryogenictemperature level from a cryogenic refrigerator to a heat load forevaporation and return,

the combination of condenser means operatively associated with saidrefrigerator to liquefy the fluid, line means communicating with thecondenser to trans- V fer the liquefied fluid to the heat load andthereby produce a refrigerating effect by boiling to a gaseous conditionadjacent to the heat load, a source of cryogenic fluid outside theclosed cycle arrangement, means accommodating the transfer of fluid fromthe source to the closed cycle arrangement when the pressure in thelatter falls below a predetermined level, other line means to transfergaseous fluid from the heat load to the condenser, said other line meanscomprising a section having parallel conduits communicating with thecondenser, filter means in each of said conduits, valve means toselectively direct cryogenic fluid through one of the filters and thenceto the condenser, means to concurrently clean the other filter, and pumpmeans associated with the line means to in duce circulation of thefluid. 6. A closed cycle arrangement according to claim 5, wherein saidsource of cryogen fluid is ambient air; said pump means including afirst pump to circulate cryogen fluid within the arrangement to thecondenser and heat load;

and a second pump communicating with ambient air,

and operative to circulate ambient air to said other conduit and therebyclean the other filter;

said valve means including a first valving element to selectivelyestablish communication between one filter, the first pump, saidcondenser and the heat load.

7. A closed cycle arrangement according to claim 6,

wherein said first valve element concurrently establishes seriescommunication between ambient air, the second pump, the other conduit,the other filter and ambient air.

8. A closed cycle arrangement according to claim 7, and including,

heating elements in the respective filters which may be energized inresponse to actuation of said valve element to heat selectively thefilters and aid in the cleaning thereof.

9. In a closed cycle arrangement to accommodate transfer 'of a cryogenfluid to a heat load for evaporation and return,

the combination of a closed cycle refrigerator having a compressionchamber and an expansion chamber, said chambers having axes in angularrelation to each other,

a large diameter piston located and reciprocally movable in thecompression chamber,

a small diameter piston located and reciprocally movable in theexpansion chamber,

a crankshaft chamber having rotatable crankshaft means therein,

power means to rotate the crankshaft means,

connecting rod means operatively linking the pistons and the crankshaftmeans,

passage means interconnecting the expansion and compression chambers,

whereby upon rotation of the crankshaft means the pistons are urged toreciprocally move in out-ofphase relationship to each other toaccommodate the transfer of a refrigerant between the chambers and toinduce refrigerant expansion in the expansion chamber and therebyproduce a refrigerating effect,

condenser means operatively associated with the expansion chamber,

a closed loop refrigerant transfer arrangement communicating with thecondenser means and having a cryogen therein,

said loop including line means establishing communication between thecondenser means and the heat load to transfer cryogen liquefied at thecondenser means to the heat load,

the boiling of said liquefied cryogen to a gaseous condition at the heatload 'being effective to produce a refrigerating effect at the load,

other line means to accommodate transfer of gaseous cryogen from theheat load to the condenser,

said other line means including pump means to induce cryogencirculation.

10. A closed cycle arrangement according to claim 9,

wherein said other line means are arranged in heat exchange relationwith the first-mentioned line means.

11. In a closed loop arrangement to transfer a liquid cryogen fluid to aheat load for evaporation and cooling of the heat load and return,

the combination of a closed cycle refrigerator having both a relativelylarge volume compression chamber and a relatively small volume expansionchamber,

the respective chambers having a first piston and a second pistonreciprocally movable therein,

a crankshaft chamber having crankshaft means rotatable therein,

connecting rod means linking said pistons and the crankshaft means toinduce piston reciprocation upon crankshaft rotation whereby the pistonsreciprocate in out-of-phase relationship to each other,

said closed cycle refrigerator including passage means extending betweenthe chambers,

said chambers and said passage means having a refrigerant therein,

the refrigerant being transferred between the chambers via the passagemeans in response to piston reciprocation and thereby produce arefrigerating effect,

condenser means forming part of the closed loop arrangement thermallyassociated with the expansion chamber,

said closed loop arrangement including a first line establishingcommunication between the condenser means and the heat load,

other line means establishing communication between the load andcondenser and including pump means to induce circulation through saidclosed loop,

said cryogen fluid being disposed in said loop and independent of therefrigerant in said chambers and said passage means,

said cryogen fluid being liquefied at the condenser means by saidrefrigerating effect,

and means to induce evaporation of a portion of said liquefied cryogenfluid whereby droplets of liquefied cryogen are entrained in evaporatedcryogen fluid and move through the first line means between thecondenser means and the heat load,

the boiling of said liquefied cryogen fluid to a gaseous condition atthe heat load being effective to produce a cooling effect at the load.

12. A closed loop arrangement to transfer a liquid cryogen fluid to aheat load for evaporation and cooling of the load and return accordingto claim 11,

and including a source of cryogen fluid normally ini2 dependent of thefluid disposed in the closed loop and,

means to establish communication between said source and said closedsystem to add cryogen fluid to the closed system when the pressure inthe latter falls below a predetermined level.

13. A closed loop arrangement to transfer a liquid cryogen fluid to aheat load for evaporation and cooling of the load and return, accordingto claim 12,

wherein said cryogen fluid is air.

14. A closed loop arrangement to transfer a liquid cryogen fluid to aheat load for evaporation and cooling of the load and return, accordingto claim 13,

wherein said other line means encircles said first line means andestablishes a heat transfer relation therebetween to induce saidevaporation of said portion of said liquefied cryogen fluid.

15. In a closed loop arrangement operative to transfer liquefied cryogenfluid from a condenser associated with a cryogenic refrigerator and to aheat load for evaporation and thereby cooling of the load and return,

said condenser being operative to liquefy the cryogen fluid in saidclosed loop arrangement,

first line means forming part of the arrangement and establishingcommunication between the condenser and the heat load,

means associated with the condenser and first line means to provide anevaporated portion of said liquefied fluid to create a dispersion ofliquefied cryogen fluid droplets within said gaseous cryogen fluid,

other line means forming part of said closed loop arrangementestablishing communication between the heat load and said condensermeans,

said other line means including pump means to induce circulation of saidcryogen fluid in said closed loop arrangement whereby the droplets ofliquefied cryogen fluid entrained in gaseous cryogen fluid aretransferred from the condenser means to the heat load,

said liquefied droplets of cryogen fluid evaporating at the heat load tothere produce a refrigerating effect,

a source of cryogen fluid normally non-communicating with the closedloop arrangement,

and control means interconnecting said source and said closed looparrangement to establish communication and accommodate transfer ofcryogen fluid from said source to said closed loop arrangement when thepressure level in said arrangement falls below a determined point.

16. A closed loop arrangement operative to transfer liquefied cryogenfluid from a condenser associated with a cryogenic refrigerator to aheat load for evaporation and thereby cooling the load and returnaccording to claim 15,

wherein said cryogen fluid is air, 7

said non-communicating source comprising air under pressure and having apressure level greater than that existent in the closed looparrangement.

References Cited UNITED STATES PATENTS 966,076 8/1910 Bobrick 62-2393,036,440 5/1962 Feinman 6264 3,125,863 3/1964 Hood 62-175 3,182,4625/1965 Long et al. 6255 3,195,322 7/1965 London 62-5l4 LLOYD L. KING,Primary Examiner,

1. IN A CLOSED CYCLE CRYOGENIC REFRIGERATOR, A COMPRESSION CHAMBER, ANEXPANSION CHAMBER, SAID CHAMBERS HAVING AXES IN ANGULAR RELATION TO EACHOTHER, A LARGE DIAMETER PISTON LOCATED IN THE COMPRESSION CHAMBER ANDRECIPROCALLY MOVABLE THEREIN, A SMALL DIAMETER PISTON LOCATED IN THEEXPANSION CHAMBER AND RECIPROCALLY MOVABLE THEREIN, CRANKSHAFT MEANS,POWER MEANS TO ROTATE THE CRANKSHAFT MEANS, CONNECTING ROD MEANSOPERATIVELY LINKING THE PISTONS TO THE CRANKSHAFT MEANS, WHEREBY UPONROTATION OF SAID CRANKSHAFT MEANS SAID PISTONS ARE URGED TO RECIPROCALLYMOVE WITHIN SAID CHAMBERS, PASSAGE MEANS INTERCONNECTING THE COMPRESSIONCHAMBER AND EXPANSION CHAMBER TO ACCOMODATE THE TRANSFER THEREBETWEEN OFA CRYOGEN, SAID PASSAGE MEANS INCLUDING HEAT TRANSFER MEANS TOACCOMODATE THE DISSIPATION OF HEAT FROM SAID CRYOGEN AS IT MOVES TO THEEXPANSION CHAMBER, SAID PISTONS BEING RECIPROCALLY MOVABLE INOUT-OF-PHASE RELATIONSHIP TO EACH OTHER WHEREBY THE EXPANSION OF THECRYOGEN IN THE EXPANSION CHAMBER PRODUCES A SUBSTANTIAL TEMPERATURE FALLTHEREIN.